Effect of dry- and wet-milled rice flours on the quality attributes of gluten-free dough and noodles

Relationship of Mixolab characteristics with protein, pasting, dynamic and empirical rheological characteristics of flours from Indian wheat varieties with diverse grain hardness

Mixolab properties of different Indian extraordinarily soft (Ex-SW), hard (HW) and medium hard (MHW) wheat varieties were evaluated and related to damaged starch content, particle size distribution, pasting, Farinographic and Mixographic properties. Water absorption (WA) of HW varieties was higher as compared to other varieties. Higher damaged starch led to more WA in HW varieties while lower in Ex-SW varieties. Unextratable polymeric protein, damaged starch and arabinoxylans were related to dough consistency. Mixolab measurement C3 (peak viscosity) and C5 (starch retrogradation) decreased with increase in grain hardness index, damaged starch content, and sodium solvent retention capacity. Dough stability (DS) and dough development time (DDT) measured by Mixolab and farinograph were significantly correlated. Mixolab parameters (C3, C4 and C5) related positively to DDT and DS while negatively to WA. HW varieties showed higher shear thinning as compared to MHW and Ex-SW varieties. C4 (hot paste stability) was lower for HW but higher for Ex-SW varieties. SuSRC was negatively related to C4 indicating that HW flours had lower starch retrogradation due to higher arabinoxylans. C3, C4 and C5 related positively to small size particles while negatively to large size particles. Slope beta (β) measured by mixolab indicated that the speed of starch gelatinization was lower for Ex-SW varieties than MHW and HW varieties.

Effect of degree of milling on physicochemical, structural, pasting and cooking properties of short and long grain Indica rice cultivars

The effects of degree of milling (DOM) between 0 and 8% on physico-chemical, structural, pasting and cooking properties of short and long grain Indica rice cultivars were studied. Ash, protein, lipids and minerals decreased while blue value and crystallinity increased with increase in DOM. The colour parameters (a∗, b∗) and cooking time (CT) decreased while L∗(lightness) increased with increase in DOM. Elongation ratio (ER), gruel solid loss (GSL), length/breadth (L/B) and paste viscosities during cooking increased with increase in DOM. Short grain rice contained lower ash, protein, lipids, Mn, K, Ca, CT and GSL than long grain while the later showed higher crystallinity, Mn, P, K, Ca and ER. Paste and dough characteristics measured using Rheometer and Mixolab, respectively correlated well and differed with cultivar and DOM. Short and long grain cultivars showed variation in loss of different chemical constituents during varied DOM causing variation in cooking characteristics.

Pasting behaviour of high impact ball milled rice flours and its correlation with the starch structure

The effects of rotational speed and milling time on pasting profile, particle size and morphology, damaged starch and gelatinization enthalpy of modified rice flours were analysed by response surface methodology to investigate the relationships among functional attributes and starch structure. Morphological changes were corroborated by scanning electron microscopy. Peak time (Pt), pasting temperature (PT), peak and final viscosities from rapid visco-analysis showed a significant decrease with increasing of milling severity. The reduction in final viscosity (FV up to 4770 mPa s), particularly for the refined flour fraction (volume median diameter, D50 < 140 µm), evidenced the poor capacity of damaged starch to bind water during heating step. In comparison with native flour, the modified flours presented higher values of damaged starch (DS 5.94-16.46%), and viscosities as well as lower values of gelatinization enthalpy (ΔH 4.67-0.71 J/g), Pt and PT denoting a lower resistance to shear stress and cooking. Such behavior is desirable in mixture design to enhance flour particles dispersion and to facilitate the interaction among food ingredients. Structural changes of starch were strongly associated to pasting behavior as it can be appreciated from the significant correlations founded: FV-DS, setback viscosity (SB)-DS, SB-D50, SB-ΔH. Planetary ball milling is a novel green method to obtain physically modified rice flours with distinctive characteristics regarding native flours, which could be well controlled by selecting suitable milling conditions. More studies should be required to expand the applications of the modified rice flours, in food and non-food products, with specific functional requirements.

A new SNP in cyOsPPDK gene is associated with floury endosperm in Suweon 542

Pyruvate orthophosphate dikinase (PPDK) is a component of glycolysis to mediate endosperm energy charge by adjusting the ratio of ATP to ADP and AMP that proposed to balance the flow of carbon into starch, protein, fatty acid and amino acid biosynthesis. However, these were inconsistent with the first report of a T-DNA insertional knockout mutant of the rice PPDK gene (flo4) showed that rice with inactivated PPDK gene failed to produce a opaque seeds. Therefore, the PPDK might have multifaceted functions in grain filling stage, which in some ways might depend on the direction of the reversible catalysis. Suweon 542 is a rice (Oryza sativa L.) mutant developed from Oryza sativa ssp. japonica cv. Namil. Suweon 542 has a milky-white floury endosperm suitable for dry filling, with low starch damage, low grain hardness, and fine flour particle size. The mutant locus on chromosome 5 controls the floury endosperm phenotype of Suweon 542. Fine mapping of this locus is required for efficient breeding of rice germplasm suitable for dry milling. In this study, whole genome of Suweon 542 and Milyang 23 were re-sequenced using Illumina HiSeq 2500. Co-segregation analysis of F_3:4 family populations derived from Suweon 542/Milyang 23 was performed using eight CAPS markers and phenotypic evaluation of the endosperm. The target region was mapped to a 33 kb region and identified to encode cytosolic pyruvate orthophosphate dikinase protein (cyOsPPDK). A G→A SNP in exon 8 of cyOsPPDK resulting in a missense mutation from Gly to Asp at amino acid position 404 was responsible for the floury endosperm of Suweon 542. qRT-PCR experiments revealed that FLO4-4 was expressed to a considerably higher level in Suweon 542 than in Namil during the grain filling stage. Overall, fine mapping of FLO4-4 and candidate gene analysis provided further insight into the floury endosperm of rice, and reveal a novel SNP in cyOsPPDK gene can affect the floury endosperm phenotype through active PPDK gene during grain filling stage.

Agronomic and genetic analysis of Suweon 542, a rice floury mutant line suitable for dry milling

BACKGROUND

Producing rice flour of good quality by dry milling is necessary to reduce milling costs and promote the processed rice food industry. This study was conducted to evaluate the dry milling properties of Suweon 542, a floury endosperm mutant, and identify the chromosomal region responsible for the floury endosperm characteristics.

RESULTS

Compared with the wild type, after dry milling process, the grain hardness of Suweon 542 was significantly lower because of its round and loosely packed starch granules. Also, the flour of Suweon 542 had significantly smaller particles and less damaged starch than Namil and other rice cultivars and its particle size distribution was similar to a commercial wheat cultivar. Considering that the yield loss of Suweon 542 due to its floury endosperm was largely compensated for by an increased number of spikelets per panicle, Suweon 542 has potential value as a raw material for rice flour production. Association analysis using 70 genome-wide SSR markers and 94 F2 plants derived from Suweon 542/Milyang 23 showed that markers on chromosome 5 explained a large portion of the variation in floury grains percentage (FGP). Further analysis with an increased number of SSR markers revealed that the floury endosperm of Suweon 542 was directed by a major recessive locus, flo7(t), located in the 19.33-19.86 Mbp region of chromosome 5, with RM18639 explaining 92.2% of FGP variation in the F2 population.

CONCLUSIONS

The floury endosperm of Suweon 542 is suitable for dry milling, with a small flour particle size and low damaged starch content. Further physical mapping of flo7(t), the floury endosperm locus of Suweon 542, would facilitate efficient breeding of rice cultivars with proper dry milling adaptability that can be used in the processed rice food industry.